Cryogenic cooling technology includes power transmission technology, medical technology, basic nuclear fusion technology, satellite-related technology, etc. using a superconductor, and has been extensively applied and developed in various fields.
In a representative cryogenic cooling method, a cooling part which performs cooling using a refrigerant such as circulating liquid nitrogen is provided at an outer side of a refrigerant container accommodating an object to be cooled, and a vacuum insulation part be provided at an outer side of the cooling part for vacuum insulation.
In this method, the object may be cooled using the refrigerant cooled to extremely low temperature, and be maintained in a cryogenic state by blocking the transfer of heat through the vacuum insulation part.
For such cryogenic cooling, a cooling condition should be maintained constant. For example, when a superconductivity condition is maintained, an electric resistance of a superconductor approaches zero and the superconductor thus has high current transfer capability even at a low voltage. However, when a cryogenic condition is canceled, the electric resistance of the superconductor sharply increases and thus normal power transmission cannot be conducted and a safety accident may occur.
Thus, in a cryogenic cooling apparatus, a cryogenic state of an object to be cooled should be stably maintained. Furthermore, whether the cryogenic state of the object is stably maintained as intended should be continuously monitored.
Thus, the cryogenic cooling apparatus may include a temperature sensor to measure temperature of the object to be cooled.
The temperature of the object to be cooled may be directly measured using the temperature sensor but the temperature of a liquid refrigerant may be directly measured using the temperature sensor. However, in many cases, the temperature sensor may be difficult to be installed at an object to be cooled or a refrigerant. Furthermore, thermal invasion through a wire used for electrical connection of a cooling sensor or the like may occur.
To solve this problem, the temperature sensor may be installed on a surface of a refrigerant container forming the cooling part, and temperature of the surface of the refrigerant container may be measured to estimate temperature of the refrigerant and determine temperature of the object to be cooled.
In this case, when the temperature sensor malfunctions or the life thereof ends, it is inevitable that a vacuum state between the refrigerant container of the cooling part and a vacuum container of the vacuum insulation part should be released to repair or exchange the temperature sensor.
The releasing of the vacuum state to repair or exchange the temperature sensor of the cryogenic cooling apparatus means that a vacuum state of an entire object to be cooled by the cryogenic cooling apparatus is released. After the exchange of the temperature sensor, the amount of time and efforts required to vacuuimize all the cryogenic cooling apparatus and a system connected thereto again are proportional to the size or scale of the system connected to the cryogenic cooling apparatus.